Despite nationwide adoption of a 21-year-old minimum legal drinking age, alcohol remains readily available to youth, who procure it from a variety of retail and social sources. Although community-level restrictions on alcohol availability to youth are increasingly important as local intervention strategies, few studies have investigated the effects of changes in alcohol availability at the local level on consumption by young people. Moreover, the processes through which changes in alcohol availability affect drinking by young people lack empirical assessment. To address these issues we propose to undertake a randomized community trial to investigate the combined effectiveness of five interventions recommended as best practices to reduce commercial and social access to alcohol among youth: (a) a reward and reminder program for retail clerks and merchants, (b) increased enforcement of sales laws through compliance checks, (c) increased enforcement of laws against adults providing alcohol to minors through a stranger purchase (shoulder tap) intervention, (d) increased enforcement of laws against underage drinking and providing alcohol to minors through a party dispersal (party patrol) program, and (e) strategic media advocacy to increase public awareness of the problems associated with underage drinking and to increase public support for the interventions. In this proposed effectiveness trial, we will randomly assign 34 Oregon communities to intervention and control conditions (17 per condition). The environmental prevention strategies will be implemented in a staggered fashion over the five-year study period. Outcome measures will be based on annual student surveys of 8th and 11th graders and biannual alcohol purchase surveys conducted in all 34 communities. Three years of baseline student survey data have already been collected. The state of Oregon will pay for Community Coordinators and related intervention costs and will work in close collaboration with the Pacific Institute for Research and Evaluation, and the Oregon Research Institute, to ensure implementation. The proposed study will test the combined effectiveness of the five interventions, will identify intervening mechanisms through which environmental interventions affect underage drinking, and will have important implications for the effective prevention of underage drinking.